The present invention relates to improvement of cutting edges of blades of a hole cutter in which each one of the blades is disposed alternately with a corresponding one of grooves in a rotational direction of the hole cutter.
FIGS. 6(a) to 8 show a prior art hole cutter. With reference to FIGS. 6(a) and 6(b), the hole cutter includes a cylindrical blade body 2 with an inner hollow space 9. Blades 4 and grooves 5 are located at a circumferential wall of the blade body 2. Each one of the blades 4 is disposed alternately with a corresponding one of the grooves 5 in a rotational direction of the blade body 2. Referring to FIG. 7, a cutting edge 8 of each blade 4 includes an outer cutting edge 10, an inner cutting edge 11, and a stepped cutting edge 12, which is located between the outer cutting edge 10 and the inner cutting edge 11. More specifically, in each cutting edge 8, the outer cutting edge 10 extends from an outermost point 13 to a corner portion 14 in a radial direction Y of the blade body 2. The inner cutting edge 10 extends from an intermediate point 15 to an innermost point 16 in the radial direction Y. The stepped cutting edge 12 extends from the corner portion 14 to the intermediate point 15 in a rotational direction X of the blade body 2. That is, the outer cutting edge 10 and the inner cutting edge 11 of each cutting edge 8 are located slightly offset from each other in the rotational direction X.
With reference to FIG. 7, the heights H15 of the intermediate points 15, which are located at radial outer positions of the inner cutting edges 11, are equal for all blades 4. Also, the heights H13 of the outermost points 13, which are located at radial outer positions of the outer cutting edges 10, are equal for all blades 4. The heights H13 and H15 are measured along the rotational axis 1a of the blade body 2 with respect to a predetermined reference plane P, which is shown in FIG. 6(a).
With reference to FIGS. 6(a), 8(a), and 8(b), when the blade body 2 is rotated as abutted against a machining material M, the machining material M is cut first by the inner cutting edge 11 of each blade 4 and then by the outer cutting edge 10 after a slight delay. FIG. 8(a) shows a momentary state in which the cutting amount with respect to the machining material M is maintained at a constant level. In this state, all inner cutting edges 11 and outer cutting edges 10 cut the machining material M to a uniform depth {circle around (1)} at the same time. FIG. 8(b) shows a momentary state in which the cutting amount with respect to the machining material M is gradually increased from the state of FIG. 8(a). In this state, like the state of FIG. 8(a), all inner cutting edges 11 and outer cutting edges 10 cut the machining material M to a uniform depth {circle around (2)} at the same time. This increases anti-cutting resistance, which is disadvantageous.
Accordingly, it is an objective of the present invention to reduce anti-cutting resistance and obtain an optimal cutting state.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a hole cutter. The hole cutter includes a cylindrical blade body with a rotational axis. The blade body includes a plurality of blades and a plurality of grooves, and each of the blades is arranged alternately with a corresponding one of the grooves around the rotational axis of the blade body. Each of the blades includes a cutting edge formed at an end of the blade. The blades include multiple types of blades with cutting edges that have different heights with respect to a predetermined reference plane perpendicular to the rotational axis.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.